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Pregnant women who have high levels of fluoride in their urine are more likely to give birth to children with lower IQ levels, a new study has found. The study, conducted by a team of researchers from the University of Toronto together with experts from the National Institute of Public Health of Mexico, University of Michigan, McGill University, Indiana University, Mount Sinai School of Medicine and Harvard School of Public Health, is the first study of this size and scope that examines the effect of fluoride exposure across multiple stages of neurodevelopment in children.

"Our study shows that the growing fetal nervous system may be adversely affected by higher levels of fluoride exposure," said Dr. Howard Hu, Professor of Environmental Health, Epidemiology and Global Health at the Dalla Lana School of Public Health, and principal investigator of the study. "It also suggests that the pre-natal nervous system may be more sensitive to fluoride compared to that of school-aged children."

For over 60 years, people living in the United States and Canada have been exposed to fluoride in their drinking water as well as dental products, which both have fluoride routinely added in order to prevent dental cavities and strengthen bones. In many other countries around the world it is also added to table salt and milk for the toted health benefits it provides. However, many argue that the health risks far outweigh any health benefits that fluoride offers, and water fluoridation needs to be abolished or at least more strictly controlled. This has fueled a greater interest by the scientific community to explore the issues, particularly the effect that exposure to fluoride has on the developing brains of young children, so that they can provide informed input so that drinking water standards can be regulated accordingly.

Previous studies have shown that continued exposure to recommended levels of fluoride in Canada and the US can cause some side effects such as mild dental staining, while exposure to fluoride at concentrations 5-10 times higher than the recommended levels can cause fluoride to accumulate in the bones — a condition known as skeletal fluorosis. Yet, according to Hu, "Relatively little is known, with confidence, about fluoride's impact on neurodevelopment."

The researchers analyzed urine samples collected from the mothers during their pregnancy, as well as urine samples collected from their children when they were between 6 and 12 years old, to get a clearer indication of the personal fluoride exposure of both the mother and their child.

"This is significant because previous studies estimated exposures based on neighborhood measurements of drinking water fluoride levels, which are indirect and much less precise measures of exposure. They also looked at children's exposures instead of prenatal exposures or had much smaller sample sizes of subjects to study," explains Dr. Hu.

The research team then examined the link between fluoride levels in urine and the verbal, quantitative and perceptual performance, as well as memory and motor skills of children at 4 years old, and again when they were between 6-12 years old. They also took other factors that are known to affect child neurodevelopment into account, including: birth weight, gestational age when born, birth order, and child's sex, as well as mother's marital status, socioeconomic status, IQ, education, age at delivery, smoking history and lead exposure.

The study found that levels of urinary fluoride where slightly higher in pregnant women compared to non-pregnant women in the US and Canada. However, according to Dr Hu, the study's findings don't provide sufficient information to suggest that there is no safe level of fluoride exposure.

"The potential risks associated with fluoride should be further studied, particularly among vulnerable populations such as pregnant women and children, and more research on fluoride's impact on the developing brain is clearly needed."